Heat softening thermally conductive compositions and methods for their preparation

ABSTRACT

A heat softening thermally conductive composition comprises: a matrix comprising a silicone resin, and a thermally conductive filler. The composition can be used as a thermal interface material in electronic devices. The composition is formulated to have any desired softening temperature.

FIELD OF THE INVENTION

[0001] This invention relates to a heat softening thermally conductive(HSTC) composition and methods for preparation and use of the same. Moreparticularly, this invention relates to a HSTC composition comprising asilicone resin system and a thermally conductive filler. The HSTCcomposition can be used as a thermal interface material (TIM).

BACKGROUND

[0002] Electronic components such as semiconductors, transistors,integrated circuits (ICs), discrete devices, and others known in the artare designed to operate at a normal operating temperature or within anormal operating temperature range. However, the operation of anelectronic component generates heat. If sufficient heat is not removed,the electronic component will operate at a temperature significantlyabove its normal operating temperature. Excessive temperatures canadversely affect performance of the electronic component and operationof the device associated therewith and negatively impact mean timebetween failures.

[0003] To avoid these problems, heat can be removed by thermalconduction from the electronic component to a heat sink. The heat sinkcan then be cooled by any convenient means such as convection orradiation techniques. During thermal conduction, heat can be transferredfrom the electronic component to the heat sink by surface contactbetween the electronic component and the heat sink or by contact of theelectronic component and heat sink with a TIM.

[0004] Surfaces of the electronic component and the heat sink aretypically not completely smooth, therefore, it is difficult to achievefull contact between the surfaces. Air spaces, which are poor thermalconductors, appear between the surfaces and increase impedance. Thesespaces can be filled by inserting a TIM between the surfaces. The lowerthe thermal resistance of the TIM, the greater the flow of heat from theelectronic component to the heat sink.

[0005] Some commercially available TIMs are elastomers filled withthermally conductive fillers. However, elastomers suffer from thedrawbacks that a high pressure is required to reduce the thermalinterfacial contact resistance and promote effective heat transferbetween the substrate and the TIM.

[0006] Silicone greases with conductive fillers have also been proposedas TIMs. However, greases suffer from the drawbacks that they can bemessy to apply and can flow out of the spaces after application.

[0007] HSTC compositions are advantageous in solving the above problemsbecause they can be handled as a solid at low temperatures and soften atan elevated temperature. The softening temperature can be equal to orabove the normal operating temperature of the electronic component.

[0008] HSTC compositions can comprise organic materials such as waxes,and conductive fillers. However, organic waxes suffer from the drawbackthat they can flow out of the spaces after application, during operationof the electronic component. Organic waxes may also be brittle at roomtemperature.

SUMMARY OF THE INVENTION

[0009] This invention relates to a heat softening thermally conductive(HSTC) composition and methods for its preparation and use. The HSTCcomposition comprises a matrix and a thermally conductive filler. Thematrix comprises a silicone resin.

DRAWINGS

[0010]FIG. 1 is an interface material according to this invention.

[0011]FIG. 2 is a device according to this invention.

REFERENCE NUMERALS

[0012]100 interface material

[0013]101 substrate

[0014]102 layer of HSTC composition

[0015]103 release liners

[0016]200 device

[0017]201 heat sink

[0018]202 second thermal interface material (TIM2)

[0019]203 electronic component

[0020]204 substrate

[0021]205 solder balls

[0022]206 first thermal interface material (TIM1)

[0023]207 metal cover

[0024]208 thermal path represented by arrows

[0025]209 chip underfill

[0026]210 pads

[0027]211 solderball array

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] All amounts, ratios, and percentages are by weight unlessotherwise indicated. The following is a list of definitions, as usedherein.

[0029] Definitions and Usage of Terms

[0030] “A” and “an” each mean one or more.

[0031] “Alkyl” means a monovalent saturated hydrocarbon group.

[0032] “Combination” means two or more items put together by any method.

[0033] “Copolymer” means a polymer made from at least two distinctmonomers. Copolymer includes, but is not limited to, polymers made fromonly two distinct monomers.

[0034] “D unit” means a unit of the formula R₂SiO_(2/2), where each R isan organic group.

[0035] “M unit” means a unit of the formula R₃SiO_(1/2), where each R isan organic group.

[0036] “Q unit” means a unit of the formula SiO_(4/2).

[0037] “Siloxane” and “silicone” are used synonymously herein.

[0038] “Silicone resin” means a polymer having a branched molecularstructure comprising R_(x)SiO_((4-x)/2) units where each R is an organicgroup; each x is 0, 1, 2, or 3; with the proviso that at least one unithas x greater than 1.

[0039] “Substituted” means one or more hydrogen atoms bonded to a carbonatom has been replaced with another substituent.

[0040] “Surface treated” means that all, or a portion of, reactivegroups on a filler particle have been rendered less reactive by anyconvenient chemical or unreactive means.

[0041] “T unit” means a unit of the formula RSiO_(3/2), where R is anorganic group.

[0042] Heat Softening Thermally Conductive Compostion

[0043] This invention relates to a HSTC composition. The HSTCcomposition comprises:

[0044] A) a matrix comprising a silicone resin,

[0045] B) a thermally conductive filler,

[0046] optionally C) a treating agent, and

[0047] optionally D) an antioxidant.

[0048] Matrix

[0049] Silicone resins are known in the art and commercially available.Silicone resins can be added to the composition in an amount of 4 to 60%of the composition. Silicone resins can comprise combinations of M, D,T, and Q units, such as DT, MDT, DTQ, MQ, MDQ, MDTQ, or MTQ resins;alternatively DT or MQ resins.

[0050] DT resins are exemplified by resins comprising the formula:(R¹R²SiO_(2/2))_(a)(R³SiO_(3/2))_(b).

[0051] Each instance of R¹, R² and R³ may be the same or different. R¹,R² and R³ may be different within each unit. Each R¹, R² and R³independently represent a hydroxyl group or an organic group, such as ahydrocarbon group or alkoxy group. Hydrocarbon groups can be saturatedor unsaturated. Hydrocarbon groups can be branched, unbranched, cyclic,or combinations thereof. Hydrocarbon groups can have 1 to 40 carbonatoms, alternatively 1 to 30 carbon atoms, alternatively 1 to 20 carbonatoms, alternatively 1 to 10 carbon atoms, alternatively 1 to 6 carbonatoms. The hydrocarbon groups include alkyl groups such as methyl,ethyl, n-propyl, isopropyl, n-butyl, and t-butyl; alternatively methylor ethyl; alternatively methyland include aromatic groups such asphenyl, tolyl, xylyl, benzyl, and phenylethyl; alternatively phenyl.Unsaturated hydrocarbon groups include alkenyl such as vinyl, allyl,butenyl, and hexenyl.

[0052] In the formula above, a is 1 to 200, alternatively 1 to 100,alternatively 1 to 50, alternatively 1 to 37, alternaively 1 to 25. Inthe formula above, b is 1 to 100, alternatively 1 to 75, alternatively 1to 50, alternatively 1 to 37, alternatively 1 to 25.

[0053] Alternatively, the DT resin may have the formula: (R¹₂SiO_(2/2))_(a)(R² ₂SiO_(2/2))_(b)(R¹SiO_(3/2))_(a)(R²SiO_(3/2))_(b),where R¹, R², a, and b are as described above. Alternatively, in thisformula, each R¹ may be an alkyl group and each R² may be an aromaticgroup.

[0054] MQ resins are exemplified by resins of the formula:(R¹R²R³SiO_(1/2))_(c)(SiO_(4/2))_(d), where R¹, R² and R³ are asdescribed above, c is 1 to 100, and d is 1 to 100, and the average ratioof c to d is 0.65 to 1.9.

[0055] A silicone polymer may be added to component A) in addition to,or instead of a portion of, the silicone resin. The silicone polymer canbe added in an amount of 0 to 35% of the composition. The siliconepolymer can be a linear or branched polydiorganosiloxane, such as apolydimethylsiloxane. Silicone polymers are exemplified by polymers ofthe formula (R¹R²R³SiO_(1/2))₂(R¹R²SiO_(2/2))_(e), where R¹, R² and R³are as described above, and e is 5 to 800, alternatively 50 to 200.

[0056] The combination of M, D, T, and Q units and the presence ofsilicone polymer influence the physical and rheological properties ofthe material. Typically, such compositions have a broad glass transitiontemperature (Tg) range. Over this range the composition undergoes asignificant decrease in modulus and viscosity with increase intemperature. This results in the gradual softening or hardening of theHSTC composition. For example, B. H. Copely, MS Thesis, University ofMinnesota, 1984 and Wengorvius, J. H.; Burnell, T. B.; Zumbrum, M. A.;Krenceski, M. A. Polym. Preprints 1998, 39(J), 512 show the effect of MQresin/silicone polymer on the glass transition temperature. For thepurposes of this invention, the silicone resin or siliconeresin/silicone polymer combination may be chosen such that it possessthe required physical integrity and modulus to be handled as a filmclose to ambient temperature. This facilitates ease of application ofthe HSTC composition as TIM in a film form. The viscosity of the matrixat room temperature can be above 100 Pascal·second (Pa·s). Concurrently,the appropriate silicone resin or silicone resin/silicone polymercombination is selected to undergo a large decrease in modulus andviscosity at operating or assembly temperature. This facilitatesintimate contact of the composition between the heat generating and heatdissipating substrates. Above 90° C., the viscosity of the matrix can bebelow 10 Pa·s.

[0057] In effect, the combination of M, D, T, and Q units on thesilicone resin or the combination of the silicone resin and siliconepolymer are selected to permit a sufficiently large change in viscositybetween the application temperature and assembly temperature oroperating temperature. The silicone resin can also be chosen to be tackyat room temperature. TIMs prepared from such matrices would beadvantageous as they would permit easy assembly.

[0058] The composition can comprise at least 4%, alternatively at least5% of component A). The composition can comprise up to 60% of componentA), alternatively up to 50%, alternatively up to 20%, alternatively upto 10%.

[0059] It should be understood that the disclosure of ranges hereinshould be taken not only to disclose the range itself but also anythingsubsumed therein, as well as endpoints. For example, disclosure of arange of 1 to 10 should be understood to disclose not only the range of1 to 10, but also 1, 2.7, 9 and 10 individually, as well as any othernumber subsumed in the range. Similarly, disclosure of a range ofhydrocarbons of 1 to 5 carbon atoms should be understood to disclose notonly hydrocarbons of 1 to 5 carbon atoms as a class, but alsohydrocarbons of 1 carbon atom, hydrocarbons of 2 carbon atoms,hydrocarbons of 3 carbon atoms, hydrocarbons of 4 carbon atoms andhydrocarbons of 5 carbon atoms individually.

[0060] Filler

[0061] Component B) is a thermally conductive filler. Component B) isdispersed in component A). The amount of component B) in the compositiondepends on various factors including the material selected for componentA), the material selected for component B), and the softeningtemperature of the composition. The amount of component B) can be atleast 40% of the overall composition, alternativley at least 50% of thecomposition, alternatively at least 80% of the composition,alternatively at least 85% of the composition. The amount of componentB) can be up to 96%, alternatively up to 95% of the composition. If theamount of component B) is too low, the composition may have insufficientthermal conductivity for some applications.

[0062] Component B) can be thermally conductive, electricallyconductive, or both. Alternatively, component B) can be thermallyconductive and electrically insulating. Suitable thermally conductivefillers for component B) include metal particles, metal oxide particles,and a combination thereof. Suitable thermally conductive fillers forcomponent B) are exemplified by aluminum nitride; aluminum oxide; bariumtitinate; beryllium oxide; boron nitride; diamond; graphite; magnesiumoxide; metal particulate such as copper, gold, nickel, or silver;silicon carbide; tungsten carbide; zinc oxide, and a combinationthereof.

[0063] Thermally conductive fillers are known in the art andcommercially available, see for example, U.S. Pat. No. 6,169,142 (col.4, lines 7-33). For example, CB-A20S and Al-43-Me are aluminum oxidefillers of differing particle sizes commercially available fromShowa-Denko, and AA-04, AA-2, and AA18 are aluminum oxide fillerscommercially available from Sumitomo Chemical Company.

[0064] Silver filler is commercially available from Metalor TechnologiesU.S.A. Corp. of Attleboro, Mass., U.S.A. Boron nitride filler iscommercially available from Advanced Ceramics Corporation, Cleveland,Ohio, U.S.A.

[0065] The shape of the filler particles is not specifically restricted,however, rounded or spherical particles may prevent viscosity increaseto an undesirable level upon high loading of the filler in thecomposition.

[0066] A combination of fillers having differing particle sizes anddifferent particle size distributions may be used as component B). Forexample, it may be desirable to combine a first aluminum oxide having alarger average particle size with a second aluminum oxide having asmaller average particle size in a proportion meeting the closestpacking theory distribution curve. This improves packing efficiency andmay reduce viscosity and enhance heat transfer.

[0067] The average particle size of the filler will depend on variousfactors including the type of filler selected for component B) and theexact amount added to the composition, however, the filler can have anaverage particle size of at least 0.2, alternatively at least 2micrometers. The filler can have an average particle size of up to 80micrometers, alternatively up to 50 micrometers.

[0068] The filler for component B) may optionally be surface treated.Treating agents and treating methods are known in the art, see forexample, U.S. Pat. No. 6,169,142 (col. 4, line 42 to col. 5, line 2).The composition may comprise at least 0.05% of C) a treating agent. TheHSTC composition may comprise up to 5%, alternatively up to 2%,alternatively up to 0.5%, of a C) treating agent.

[0069] The treating agent can be an alkoxysilane having the formula: R⁴_(f)Si(OR⁵)_((4-f)), where f is 1, 2, or 3; alternatively x is 3. R⁴ isa substituted or unsubstituted monovalent hydrocarbon group of at least1 carbon atom, alternatively at least 8 carbon atoms. R⁴ has up to 50carbon atoms, alternatively up to 30 carbon atoms, alternatively up to18 carbon atoms. R⁴ is exemplified by alkyl groups such as hexyl, octyl,dodecyl, tetradecyl, hexadecyl, and octadecyl; and aromatic groups suchas benzyl and phenylethyl. R⁴ can be saturated or unsaturated, branchedor unbranched, and unsubstituted. R⁴ can be saturated, unbranched, andunsubstituted.

[0070] R⁵ is an unsubstituted, saturated hydrocarbon group of at least 1carbon atom. R⁵ may have up to 4 carbon atoms, alternatively up to 2carbon atoms. Component C) is exemplified by hexyltrimethoxysilane,octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethyoxysilane,tetradecyltrimethoxysilane, phenyltrimethoxysilane,phenylethyltrimethoxysilane, octadecyltrimethoxysilane,octadecyltriethoxysilane, and a combination thereof.

[0071] Alkoxy-functional oligosiloxanes can also be used as treatmentagents. Alkoxy-functional oligosiloxanes and methods for theirpreparation are known in the art, see for example, EP 1 101 167 A2. Forexample, suitable alkoxy-functional oligosiloxanes include those of theformula (R⁶⁰)_(g)Si(OSiR⁷ ₂R⁸)_(4-g). In this formula, g is 1, 2, or 3,alternatively g is 3. Each R⁶ can be an alkyl group. Each R⁷ is can beindependently selected from unsaturated monovalent hydrocarbon groups of1 to 10 carbon atoms. Each R⁸ can be an unsaturated monovalenthydrocarbon group having at least 111 carbon atoms.

[0072] Treatment agents can also include alkylthiols such as octadecylmercaptan and others, fatty acids such as oleic acid, stearic acid, andalcohols such as myristyl alcohol, cetyl alcohol, stearyl alcohol, or acombination thereof.

[0073] Treatment agents for alumina or passivated aluminum nitride couldinclude alkoxysilyl functional alkylmethyl polysiloxanes (e.g., partialhydrolysis condensate of R⁹ _(h)R¹⁰ _(i)Si(OR¹¹)(4-h-i) or cohydrolysiscondensates or mixtures), similar materials where the hydrolyzable groupwould be silazane, acyloxy or oximo. In all of these, a group tetheredto Si, such as R⁹ in the formula above, is a long chain unsaturatedmonovalent hydrocarbon or monovalent aromatic-functional hydrocarbon.R¹⁰ is a monovalent hydrocarbon group, and R¹¹ is a monovalenthydrocarbon group of 1 to 4 carbon atoms. In the formula above, h is 1,2, or 3 and i is 0, 1, or 2, with the proviso that h+i is 1, 2, or 3.One skilled in the art could optimize a specific treatment to aiddispersion of the filler without undue experimentation.

[0074] Other Optional Components

[0075] Component B), the thermally conductive filler, may optionallycomprise a reinforcing filler in addition to the thermally conductivefiller, or instead of a portion of the thermally conductive filler. Thereinforcing filler can be a chopped fiber, such as chopped KEVLAR®.Without wishing to be bound by theory, it is thought that choppedKEVLAR® improves strength and coefficient of thermal expansion (CTE).Reinforcing fillers may also be treated with component C).

[0076] Optional component D) is an antioxidant. Without wishing to bebound by theory, it is thought that component D) prevents chain cleavageor decomposition of the silicone resin, the silicone polymer, or thefiller treating agent. Component D) can comprise any antioxidantcommonly used in plastics such as polypropylene. Component D) can beadded to the composition in an amount of at least 0.001%, alternativelyat least 0.05% up to 1%.

[0077] Suitable antioxidants are known in the art and commerciallyavailable. Suitable antioxidants include phenolic antioxidants andcombinations of phenolic antioxidants with stabilizers. Phenolicantioxidants include fully sterically hindered phenols and partiallyhindered phenols. Stabilizers include organophosphorous derivatives suchas trivalent organophosphorous compound, phosphites, phosphonates, and acombination thereof; thiosynergists such as organosulfur compoundsincluding sulfides, dialkyldithiocarbamate, dithiodipropionates, and acombination thereof; and sterically hindered amines such astetramethyl-piperidine derivatives. Suitable antioxidants andstabilizers are disclosed in Zweifel, Hans, “Effect of Stabilization ofPolypropylene During Processing and Its Influence on Long-Term Behaviorunder Thermal Stress,” Polymer Durability, Ciba-Geigy AG, AdditivesDivision, CH-4002, Basel, Switzerland, American Chemical Society, vol.25, pp. 375-396, 1996.

[0078] Suitable phenolic antioxidants include vitamin E and IRGANOX®1010 from Ciba Specialty Chemicals, U.S.A. IRGANOX® 1010 comprisespentaerythriol tetrakis(3-(3,5-di-tbutyl-4-hydroxyphenyl)propionate).

[0079] Optional component E) is an inhibitor. Component E) can be anaddition reaction catalyst inhibitor. Addition reaction catalystinhibitors are known in the art and commercially available, see forexample, U.S. Pat. No. 5,929,164 (col. 1, line 65 to col. 3, line 65).

[0080] Component E) can be a phosphine, a diphosphine, an amine, adiamine, a triamine, an organic sulfide, an alkenyl-functional compound,an alkynyl-functional compound, a hydroxy-functional compound, acombination thereof, or any other transition metal catalyst poison.

[0081] Suitable phosphines include trialkyl phosphines and triarylphosphines such as triphenyl phosphine. Suitable diphosphines includetetraphenylethylene diphosphine. Suitable amines include n-butyl amineand triethanolamine. Suitable diamines include tetramethylenediamine.Suitable organic sulfides include ethyl phenyl sulfide. Suitablealkenyl-functional compounds can be organic, organosilicones, ororganosilanes. Suitable alkenyl-functional compounds includevinylsiloxanes and vinylsilanes. Suitable alkynyl functional compoundscan be organic, such as acetylene, propyne, 1-butyne, 1-pentyne,4,4-dimethyl-1-pentyne, 1-hexyne, 5-methyl-1-hexyne, and 1-decyne.

[0082] Component E) is added in an amount sufficient to providemechanical and chemical stability to the HSTC composition for a periodof at least 7 years when the composition is to be used in a centralprocessing unit (CPU) device. The amount of component E) can be at least0.001%. The amount of component E) can be up to 1%.

[0083] Component F) is an optional matrix material that can be added inaddition to component A) or instead of a portion of component A).Component F) can comprise an organofunctional silicone wax, asilicone-organic block copolymer, or a combination thereof.

[0084] Component G) is a vehicle such as a solvent or diluent. ComponentG) can be added during preparation of the composition, for example, toaid mixing and delivery. All or a portion of component G) may optionallybe removed after the HSTC composition is prepared.

[0085] Component H) is a wetting agent.

[0086] Component I) is an antifoaming agent.

[0087] Component J) is a pigment.

[0088] Component K) is a flame retardant.

[0089] Component L) is a spacer. Spacers can comprise organic particles,inorganic particles, or a combination thereof. Spacers can be thermallyconductive, electrically conductive, or both. Spacers can have aparticle size of at least 25 micrometers up to 250 micrometers. Spacerscan comprise monodisperse beads. The amount of component L) depends onvarious factors including the distribution of particles, pressure to beapplied during placement, and temperature of placement. The compositioncan contain up to 15%, alternatively up to 5% of component L) added inaddition to, or instead of, a portion of component B).

[0090] Component M) is a low melting metal filler. The low melting metalfiller can comprise In, Sn, or an alloy thereof. The low melting metalfiller may optionally further comprise Ag, Bi, Cd, Cu, Ga, Pb, Zn, or acombination thereof. Examples of suitable low melting metal fillersinclude In—Bi—Sn alloys, Sn—In—Zn alloys, Sn—In—Ag alloys, Sn—Ag—Bialloys, Sn—Bi—Cu—Ag alloys, Sn—Ag—Cu—Sb alloys, Sn—Ag—Cu alloys, Sn—Agalloys, Sn—Ag—Cu—Zn alloys, and combinations thereof. The low meltingmetal filler can have a melting point of up to 250° C., alternatively upto 225° C. The low melting metal filler can have a melting point of atleast 50° C., alternatively at least 150° C. The low melting metalfiller can be a eutectic alloy, a non-eutectic alloy, or a pure metal.Low melting metal fillers are known in the art and commerciallyavailable. Component M) can be added in addition to, or instead of, allor a poriton of component B). The composition may contain up to 96% ofcomponent M).

[0091] Method of Preparation of the Heat Softening Thermally ConductiveComposition

[0092] Component A) is selected such that the composition can be handledas a solid at room temperature and deformable at or above assemblytemperature of the electronic device.

[0093] The HSTC composition can be formulated to have a thermalconductivity of at least 0.8 Watts per meter Kelvin (W/mK),alternatively at least 2 W/mK. Thermal conductivity depends on variousfactors including the amount and type of filler selected for componentB).

[0094] The HSTC composition can be prepared by any convenient means,such as mixing all components at a temperature higher than the softeningtemperature

[0095] When component C) is present, the HSTC composition may optionallybe prepared by surface treating component B) with component C) andthereafter mixing the composition at a temperature above the softeningtemperature. Alternatively, component C) may be mixed with some or allof the other components simultaneously at a temperature above thesoftening temperature.

[0096] When component G) is present, the composition can be prepared bymixing all components at ambient or elevated temperature.

[0097] Methods of Use

[0098] The HSTC composition described above can be used as an interfacematerial, such as a thermal interface material (TIM). The interfacematerial may have any convenient configuration, and one skilled in theart would be able to control the configuration by appropriate selectionof component A), and other components. The HSTC composition can beformulated to be form stable under ambient conditions. The HSTCcomposition can be formulated to be self-supporting under ambientconditions. The HSTC composition may optionally be provided as a flatmember, such as a pad, tablet, sheet, or tape. Alternatively, the HSTCcomposition may be provided as a hemispherical nubbin, a convex member,a pyramid, or a cone. Without wishing to be bound by theory, it isthought that component A) can make HSTC composition a tacky solid underambient conditions, and that the tackiness will be advantageous inapplication of the HSTC composition to a substrate.

[0099] The HSTC composition may optionally have a removable releasesheet over a surface. A release sheet can be used when the HSTCcomposition is tacky at ambient conditions. The release sheet can be,for example, a wax- or silicone-coated paper or plastic sheet having arelatively low surface energy. The HSTC composition may be applied to aface stock, liner, or other release sheet by any conventional means suchas a direct process, e.g., spray-coating, knife-coating, roller coating,casting, drum coating, dipping or the like or an indirect transferprocess using a release sheet. A solvent, diluent, or other vehicle maybe added to the HSTC composition before application, and thereafter thevehicle is removed to leave an adherent film, coating, or residue of theHSTC composition on the release sheet.

[0100] The HSTC composition may optionally be coated on a substrate, forexample, when the HSTC composition lacks sufficient form stabilityduring processing. The substrate can be a thermally conductive material,an electrically conductive material, or both. The substrate can be, forexample, a metal foil or perforated metal foil, such as gold, silver,copper, or aluminum foil; polyimide; polyamide; KAPTON®) from E. I. DuPont de Nemours and Company, Inc., of Wilmington, Del., U.S.A.; orpolyethylene terephthalate polyester (MYLAR® from E. I. Du Pont deNemours and Company, Inc., of Wilmington, Del., U.S.A.). The compositioncan be coated on one or more surfaces of the substrate. Release sheetsmay be used on both sides of the coated substrate. This interfacematerial is shown in FIG. 1. In FIG. 1, the interface material 100comprises a substrate 101, and layers of the HSTC composition describedabove 102 formed on opposing sides of the substrate 101. Release liners103 are applied over the exposed surfaces of the HSTC composition 102.

[0101] Various interface materials comprising the HSTC compositiondescribed above can be prepared. The HSTC composition described abovecan be used to prepare interface materials by various methods, includingthose disclosed in U.S. Pat. Nos. 4,299,715 and 5,904,796.

[0102] The HSTC composition can be interposed along a thermal pathbetween a heat source a heat spreader. The HSTC composition can beinterposed by any convenient means, such as applying a form stable HSTCcomposition or interface material comprising the HSTC compositionbetween the heat source and the heat spreader with or without anadhesive or primer, hot-melt dispensing the HSTC composition, or solventcasting the HSTC composition.

[0103] The heat source can comprise an electronic component such as asemiconductor, a transistor, an integrated circuit, or a discretedevice.

[0104] The heat spreader can comprise a heat sink, a thermallyconductive plate, a thermally conductive cover, a fan, a circulatingcoolant system, a combination thereof, or others. The HSTC compositioncan be used in direct contact with the electronic component and the heatsink. The HSTC composition can be applied either to the electroniccomponent and thereafter the heat sink, or the HSTC composition can beapplied to the heat sink and thereafter to the electronic component.

[0105] During or after interposing the HSTC composition along thethermal path, the HSTC composition can be heated to a temperature equalto or greater than the softening temperature. Pressure may be applied.The HSTC composition can then be cooled.

[0106] This invention further relates to a product comprising:

[0107] a) an electronic component,

[0108] b) an interface material, and

[0109] c) a heat sink;

[0110] where the interface material is arranged along a thermal pathextending from a surface of the electronic component to a surface of theheat sink, where the interface material comprises the compositiondescribed above.

[0111] This invention further relates to a product comprising:

[0112] a) a heat spreader, and

[0113] b) an interface material on a surface of the heat spreader,

[0114] where the interface material and the heat spreader are configuredto comprise a portion of a thermally conductive path between anelectronic component and a heat sink, and where the interface materialcomprises the composition described above.

[0115]FIG. 2 shows a device 200 according to this invention. The device200 comprises an electronic component (shown as an integrated circuit(IC) chip) 203 mounted to a substrate 204 by a solderball array 211 andchip underfill 209. The substrate 204 has solder balls 205 attachedthereto through pads 210. A first interface material (TIM1) 206 isinterposed between the IC chip 203 and a metal cover 207. The metalcover 207 acts as a heat spreader. A second interface material (TIM2)202 is interposed between the metal cover 207 and a heat sink 201. Heatmoves along a thermal path represented by arrows 208 when the device isoperated.

[0116] Products and devices may be prepared including the HSTCcomposition described above. For example, the HSTC composition describedabove may be used as the thermally conductive interface materials in thedevices disclosed in U.S. Pat. Nos. 5,912,805; 5,930,893; 5,950,066;6,054,198; and 6,286,212 in addition to, or instead of, the interfacematerials described therein.

EXAMPLES

[0117] These examples are intended to illustrate the invention to oneskilled in the art and should not be interpreted as limiting the scopeof the invention set forth in the claims. Me represents a methyl groupand Ph represents a phenyl group.

Reference Example 1 Laser Flash Method

[0118] Thermal impedance measurement of the thermal interface materialsare carried out on the Holometrix Microflash 300 equipment (HolometrixMicromet, Bedford, Mass.; now NETZSCH Instruments, Inc.). Silicon wafersfor use in the sample preparation are obtained from Addison Engineering,Inc. of San Jose, Calif. The silicon wafers are diced to 8±0.13millimeter (mm) square substrates and are deionized water rinsed bySilicon Sense of Nashua, N.H.

[0119] These silicon wafers are used as substrates to prepare testassemblies for measurement of thermal impedance. To test the thermalimpedance, a layer of the HSTC composition is placed on one siliconsubstrate. A second silicon substrate is placed on top of the HSTCcomposition to form a sandwiched assembly. A compressive force isapplied on the assemblies at different temperatures to monitor the flowof the HSTC composition and measure the resulting bondline thicknessunder the compressive force/temperature conditions.

[0120] The thermal impedance of the assemblies is measured by laserflash methodology. The laser flash method involves rapidly heating oneside of the assembly with a single pulse from a laser and monitoring thearrival of the resulting temperature disturbance as a function of timeon the opposite surface. The thermal impedance of the thin TIM betweenthe two substrates is measured using multi-layer analysis. Technicaldetails of the method can be found in the instrument manual, as well asin publications by Campbell, R. C.; Smith, S. E.; Dietz, R. L.,“Measurements of Adhesive Bondline Effective Thermal Conductivity andThermal Resistance Using the Laser Flash Method,” IEEE SEMI-THERM XVSymposium, (1999) pages 83-97; Campbell, R. C.; Smith, S. E.; Dietz, R.L “Laser Flash Diffusivity Measurements of Filled Adhesive EffectiveThermal Conductivity and Contact Resistance Using Multilayer Methods,”Thermal Conductivity 25—Thermal Expansion 13, Jun. 13-16, 1999; and“Standard Test Method for Thermal Difusivity of Solids by the FlashMethod,” ASTM Test Method E1461-92.

Reference Example 2 Measurement of Viscosity

[0121] The measurement of complex viscosity of the compositions as afunction of temperature is obtained on an Advanced Rheometric ExpansionSystem (ARES) Rheometer from Rheometric Scientific, Piscataway, N.J.,USA. The data is recorded by cooling the composition between 25 mmparallel plates from 90 to 30° C., under a dynamic strain of 0.5%,frequency of 1 radian/second, and a cooling rate of 2° C./minute.

Example 1

[0122] A silicone resin of the formula:(Ph₂SiO_(2/2))₁₉(Me₂SiO_(2/2))₁₉(PhSiO_(3/2))₃₇(MeSiO₃₁₂)₂₅ is combinedwith Al₂O₃ filler (2:1 mixture of CB-A20S and Al-43-Me aluminum oxidefillers from Showa-Denko K.K.) by heating the resin and filler to 80° C.and centrifugal mixing. The mixture has 85.65 weight % filler loading.

[0123] The complex viscosity of the resulting HSTC composition asmeasured on the rheometer under conditions described in ReferenceExample 2 is 7,376 Pa·s at 30° C. and −10 Pa·s at 90° C. The HSTCcomposition can be pressed between two release liners to form-stable,tacky, flexible, 6 mil thick film at room temperature

[0124] The HSTC composition is used to prepare assemblies between twosilicon substrates as described in Reference Example 1. The bondlinethickness of the HSTC composition within the assembly at 90° C., underdifferent compressive pressure is listed in Table 1, along with thethermal impedance as measured by laser flash at those bondlinethicknesses. TABLE 1 Pressure Bondline Thickness Thermal Impedance(KiloPascals) (kPa) (micrometers) (μm) (cm² ° K/W)  28 74 0.45 138 520.40

Example 2

[0125] A silicone resin of the formula:(Ph₂SiO_(2/2))₁₉(Me₂SiO_(2/2))₁₉(PhSiO_(3/2))₃₇(MeSiO_(3/2))₂₅ iscombined with Al₂O₃ filler (2:1 mixture of CB-A20S and Al-43-Me aluminumoxide fillers from Showa-Denko K.K.) by heating the resin and filler to80° C. and centrifugal mixing. The mixture has 88.08 weight % fillerloading.

[0126] The complex viscosity of the resulting HSTC composition asmeasured on the rheometer under conditions described in ReferenceExample 2 is 13,932 Pa·s at 30° C. and 190 Pa·s at 90° C. The HSTCcomposition can be pressed between two release liners to form-stable,tacky, flexible, 6 mil thick film at room temperature

[0127] The HSTC composition was used to prepare assemblies between twosilicon substrates as described in Reference Example 1. The bondlinethickness of the HSTC composition within the assembly at 90° C., underdifferent compressive pressure is listed in Table 2, along with thethermal impedance as measured by laser flash at those bondlinethicknesses. TABLE 2 Pressure Bondline Thickness Thermal Impedance (kPa)(μm) (cm² ° K/W)  28 103 0.54 138  90 0.44

Example 3

[0128] A silicone resin/silicone polymer blend consisting of (i) 61.08%by weight of an organopolysiloxane resin consisting of (CH₃)₃SiO_(1/2)siloxane units and SiO_(4/2) siloxane units, wherein the resin has anumber-average molecular weight of 2,600, the mole ratio of(CH₃)₃SiO_(1/2) units to SiO_(4/2) units is 0.9:1, and the resincontains less than 1 percent by weight of silicon-bonded hydroxyl groupsand (ii) 38.92% by weight of a dimethylvinylsiloxy-terminatedpolydimethylsiloxane having a viscosity of about 0.3 to 0.6 Pascalseconds (Pa s) at 25° C. is used as the matrix in this example. Theabove resin/polymer blend is mixed with Al₂O₃ filler (2:1 mixture ofCB-A20S and Al-43-Me aluminum oxide fillers from Showa-Denko K.K.) andStearic Acid (Aldrich Chemical Company) as filler treating agent byheating the resin and filler to 80° C. and centrifugal mixing. Themixture contains 88.08 weight % filler, 0.6 weight % stearic acid, and11.32 weight % of the matrix.

[0129] The complex viscosity of the resulting HSTC composition asmeasured on the rheometer under conditions described in ReferenceExample 2 is 96,691 Pa·s at 30° C. and 1,996 Pa·s at 90° C. Theresulting HSTC composition can be pressed between two release liners toform-stable, tacky, flexible, 6 mil thick film at room temperature.

[0130] The HSTC composition is used to prepare assemblies between twosilicon substrates as described in Reference Example 1. The bondlinethickness of the HSTC composition within the assembly at 90° C., underdifferent compressive pressure is listed in Table 3, along with thethermal impedance as measured by laser flash at those bondlinethicknesses. TABLE 3 Pressure Bondline Thickness Thermal Impedance (kPa)(μm) (cm² ° K/W)  28 92 0.43 138 74 0.37

Example 4

[0131] A silicone resin of the formula: (Ph₂SiO_(2/2))₁₉(Me₂SiO_(2/2))1₉(PhSiO_(3/2))₃₇(MeSiO_(3/2))₂₅ is combined with Boron Nitride filler(PT350S from Advanced Ceramics Corporation) by heating the resin andfiller to 100° C. and centrifugal mixing. The mixture has 54.87 weight %filler loading.

[0132] The complex viscosity of the resulting HSTC composition asmeasured on the rheometer under conditions described in ReferenceExample 2 is 455,640 Pa·s at 30° C. and 10,058 Pa·s at 90° C. Theresulting HSTC composition can be pressed between two release liners toform-stable, tacky, flexible, 6 mil thick film at room temperature

[0133] The HSTC composition is used to prepare assemblies between twosilicon substrates as described in Reference Example 1. The bondlinethickness of the material within the assembly at 90° C., under differentcompressive pressure is listed in Table 4, along with the thermalimpedance as measured by laser flash at those bondline thicknesses.TABLE 4 Pressure Bondline Thickness Thermal Impedance (kPa) (μm) (cm² °K/W)  28 190 1.33 138 163 0.89

1. A composition comprising: A) a matrix comprising i) 4 to 60% based onthe weight of the composition of a silicone resin, and ii) 0 to 35%based on the weight of the composition of a silicone polymer; B) 40 to96% based on the weight of the composition of a thermally conductivefiller; C) 0 to 5% based on the weight of the composition of a treatingagent; and D) 0 to 1% based on the weight of the composition of anantioxidant.
 2. The composition of claim 1, where the composition isformulated to soften and flow at a temperature of at least 40° C.
 3. Thecomposition of claim 1, where component i) comprises a DT resin, an MQresin, or a combination thereof.
 4. The composition of claim 1, wherecomponent i) comprises a DT resin comprising:(R¹R²SiO_(2/2))_(a)(R³SiO_(3/2))_(b), where each R¹ independentlyrepresents a hydroxyl group or an organic group, each R² independentlyrepresents a hydroxyl group or an organic group, each R³ independentlyrepresents a hydroxyl group or an organic group, a is at least 1, a isup to 200, b is at least 1, and b is up to
 100. 5. The composition ofclaim 4, where each R¹ is independently phenyl, tolyl, xylyl, benzyl,phenethyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, or t-butyl; eachR² is independently phenyl, tolyl, xylyl, benzyl, phenethyl, methyl,ethyl, n-propyl, isopropyl, n-butyl, or t-butyl; each R³ isindependently phenyl, tolyl, xylyl, benzyl, phenethyl, methyl, ethyl,n-propyl, isopropyl, n-butyl, or t-butyl; a is at least 1; a is up to100; b is at least 1; and bis up to
 75. 6. The composition of claim 1,where component i) comprises a DT resin of the formula: (R¹₂SiO_(2/2))_(a)(R² ₂SiO_(2/2))_(b)(R¹SiO_(3/2))_(c)(R²SiO_(3/2))_(d),where each R¹ independently represents a hydroxyl group or an organicgroup, each R² independently represents a hydroxyl group or an organicgroup, a is at least 1, a is up to 100, b is at least 1, and b is up to100.
 7. The composition of claim 1, where component i) comprises an MQresin comprising: (R¹R²R³ SiO_(1/2))_(c)(SiO_(4/2))_(d), each R¹independently represents a hydroxyl group or an organic group, each R²independently represents a hydroxyl group or an organic group, each R³independently represents a hydroxyl group or an organic group, c is atleast 1, c is up to 100, d is at least 1, d is up to 100, and averageratio of c/d is 0.65 to 1.9.
 8. The composition of claim 1, wherecomponent ii) is present and has the formula: (R¹R²R³SiO_(1/2))₂(R¹R²SiO_(2/2))_(e), where each R¹ independently represents a hydroxylgroup or an organic group, each R² independently represents a hydroxylgroup or an organic group, each R³ independently represents a hydroxylgroup or an organic group, e is at least 5, and e is up to
 800. 9. Thecomposition of claim 8, where component ii) is a polydiorganosiloxane.10. The composition of claim 1, where component B) is electricallyconductive.
 11. The composition of claim 1, where component B) iselectrically insulating.
 12. The composition of claim 1, where componentB) comprises aluminum nitride, aluminum oxide, barium titinate,beryllium oxide, boron nitride, diamond, graphite, magnesium oxide,metal particulate, silicon carbide, tungsten carbide, zinc oxide, or acombination thereof.
 13. The composition of claim 1, where component C)is present and comprises an alkoxysilane having the formula: R⁴_(f)Si(OR⁵)_((4-f)), where R⁴ is a substituted or unsubstitutedmonovalent hydrocarbon group of at least 1 carbon atoms and up to 50carbon atoms, each R⁵ is independently an unsubstituted, saturatedhydrocarbon group of at least 1 carbon atom and up to 4 carbon atoms,and f is 1, 2, or
 3. 14. The composition of claim 1, where component C)is present and comprises an alkoxysilane, an alkoxy-functionaloligosiloxane, an alkylthiol, a fatty acid, an alcohols, or acombination thereof.
 15. The composition of claim 1, where component D)is present and comprises a phenolic antioxidant or a combination of aphenolic antioxidant and a stabilizer.
 16. The composition of claim 1,further comprising an optional component comprising E) an inhibitor, areinforcing filler; F) can comprise an organofunctional silicone wax, asilicone-organic block copolymer, or a combination thereof.; G) avehicle; H) a wetting agent; I) an antifoaming agent; J) a pigment; K) aflame retardant; L) a spacer; M) a low melting metal filler; or acombination thereof.
 16. An interface material comprising I) thecomposition of claim 1, where the composition is formed as a flatmember, a hemispherical nubbin, a convex member, a pyramid, or a cone.17. The interface material of claim 16, further comprising II) a releasesheet, where the release sheet covers a surface of the composition. 18.The interface material of claim 18, where the composition is coated on asurface of a substrate.
 19. The interface material of claim 18, wherethe substrate comprises a metal foil, a perforated metal foil, apolyamide sheet, a polyimide sheet, or a polyethylene terephthalatepolyester sheet.
 20. The interface material of claim 19, where thecomposition is coated on two sides of the substrate.
 21. The interfacematerial of claim 18, further comprising II) a release sheet covering asurface of the composition opposite the substrate.
 22. A methodcomprising: i) interposing the composition of claim 1 along a thermalpath between a heat source and a heat spreader.
 23. The method of claim22, wherein the heat source comprises an electronic component.
 24. Themethod of claim 22, where the heat spreader comprises a heat sink, athermally conductive plate, a thermally conductive cover, a fan, or acirculating coolant system.
 25. The method of claim 22, furthercomprising: ii) heating the composition to a temperature equal to orgreater than softening temperature of the composition, and iii) applyingpressure to the composition.
 26. The method of claim 25, furthercomprising: iv) cooling the composition to a temperature less than thephase change temperature.
 27. A device comprising: a) an electroniccomponent, b) an interface material, and c) a heat sink; where theinterface material is arranged along a thermal path extending from asurface of the electronic component to a surface of the heat sink, wherethe interface material comprises the composition of claim
 1. 28. Adevice comprising: a) a heat spreader, and b) an interface material on asurface of the heat spreader, where the interface material and the heatspreader are configured to comprise a portion of a thermally conductivepath between an electronic component and a heat sink, and where theinterface material comprises the composition of claim 1.